Conventionally, as disclosed in JP-A7-74062, for example, such kind of capacitor element is manufactured as follows.
First, as shown in FIG. 4, valve metal powder such as tantalum powder is compacted into a porous chip body 2 so that an anode bar 3 is fixed to an end surface 2a of the chip body 2, and then the chip body is heated to a high temperature for sintering the valve metal powder.
Subsequently, as shown in FIG. 5, a highly insulating dielectric film 4 of e.g. tantalum pentoxide is formed on particle surfaces of the valve metal powder constituting the chip body 2 so that the dielectric film extends up to the obverse surface of the anode bar 3.
Then, as shown in FIG. 6, a solid electrolyte layer 5 of a conductive polymer is formed on the dielectric film 4.
Subsequently, as shown in FIG. 7, a cathode film 6 having a two-layer structure consisting of a graphite layer as the underlying layer and a metal layer as the upper layer is formed on the solid electrolyte layer 5, whereby the capacitor element 1 is provided.
As disclosed in JP-A 60-220922, for example, and shown in FIG. 8, the capacitor element 1 manufactured in the above-described manner is placed between a pair of lead terminals 7 and 8. The anode bar 3 of the capacitor element 1 is fixed to the lead terminal 7 by e.g. welding, whereas the other lead terminal 8 is connected to the cathode film 6 of the chip body 2, and the entirety is sealed in a package body 9 made of a synthetic resin. In this way, a solid electrolytic capacitor 10 as a finished product is provided.
In the capacitor element 1, the anode bar 3 projects from the end surface 2a of the chip body 2. Therefore, in the process of assembling the capacitor element 1 into the solid electrolytic capacitor 10, stress is exerted on the root portion of the anode bar 3 connected to the end surface 2a of the chip body 2. The stress may produce a crack in the dielectric film 4 on the end surface 2a of the chip body 2.
The crack formed in the dielectric film 4 causes electrical connection between the solid electrolyte layer 5 formed on the dielectric film 4 and the valve metal particles (anode side), which considerably increases the possibility that the capacitor element becomes defective before the element is assembled into the solid electrolytic capacitor 10.